Method of treating a part in order to alter at least one of the properties thereof

ABSTRACT

Process for the treatment of a component, at least one zone to be treated of which located in the depth of this component at a certain distance from the surface thereof, has at least one property that can be modified when this zone is subjected to a thermal energy density above a specified treatment level, consisting: in placing the component ( 1 ) to be treated at a thermal energy level below said specified level ( 7 ); and in subjecting, through its aforementioned surface, for a specified time and in the form of at least one pulse, said component to a power flux ( 4 ) generated by a particle emission means ( 3 ), this emission means being regulated so as to produce a thermal energy density ( 5 ) that is concentrated on or has a localized maximum in said zone to be treated and reaching, in at least part of this zone, a level above said specified treatment level.

The invention relates to the general technical field of the treatment ofmaterials.

PRIOR ART

In the prior art, there are various types of processes for treating thesurface of components, the objective of which is to convert the physicaland/or physico-chemical properties and/or the composition and/or therelief of a surface layer of the material. In these processes, thetreatment affects the surface and possibly a thickness of the materiallying between the surface and a certain depth.

Among these surface treatment processes are, for example, processes thatuse the deposition of thin films, chemical or mechanical treatments,surface-localized heat treatments, bombardment by particles or byphotons and treatments that combine one or other of these processes.Whatever the type of treatment used, the objective is to affect thematerial on its surface and in a layer flush with the surface.

Some of these processes make use, at least in part, of an increase inthe thermal energy (i.e. the energy associated with raising thetemperature and/or the energy associated with phase changes and/orchemical reactions), which is located at the surface and in a layer thatincludes the surface, as driving force for converting the properties ofthe material on the surface. Thus, to produce such increases in thermalenergy, energy is deposited locally in the surface layer by means oflaser beams, electron beams or ion beams.

United States patent US-RE-036760 discloses a surface treatment processin which an ion beam is used repeatedly to treat the surface of amaterial.

U.S. Pat. No. 6,086,726 discloses a method of modifying a surface andcomprises the deposition of a coating on the surface of a material. Thissurface thus coated is then subjected to an ion beam characterized by anumber of pulses, an ion type and a fluence level.

U.S. Pat. No. 6,049,162 discloses an example of an electron beam sourceand its use for surface treatment.

U.S. Pat. No. 4,927,992 discloses a method of manufacturing articlesfrom metal powder using a focused particle beam having an energy densitysufficient to melt the powder. This beam constructs the article inquestion layer by layer, by melting a layer of powder and the upper partof the underlying substrate at the points where the beam passes. Aftercooling, the melted layer of powder becomes the new substrate. Powder isfed in so that the beam always sees a layer of powder of sufficientthickness. The article is thus constructed layer by layer.

U.S. Pat. No. 4,370,175 discloses a method of manufacturing photovoltaiccells, in which a p/n junction is created by implantation and thematerial of the surface crust is annealed by means of a pulsed laserbeam whose wavelength lies in the ultraviolet, with a pulse energy of atleast two joules.

U.S. Pat. No. 4,370,176 discloses a process in which a substrate isbombarded with particles of a doping material so as to be able toproduce local surface liquefaction of the substrate, so that, afterresolidification, the defects created in the surface crust by thebombardment are removed and so that the particles can be positioned insubstitutional sites completely integrated into the crystal lattice ofthe substrate.

U.S. Pat. No. 5,918,140 discloses a process in which a thin layer ofdopant atoms is deposited and then melted down to a desired depth bymeans of a laser impulse or an ion beam.

U.S. Pat. No. 5,445,689 discloses a process in which an ion beam is usedto melt the surface of a material so as to change its structure and thusincrease its corrosion resistance. Optionally, the material is coatedbefore the ion beam treatment with a film capable of forming an alloywith the material.

In the prior art, there are also processes whose objective is to modifya material in a layer located in the depth, below the surface, in whichthe mechanism of transforming the physical properties is essentially dueto the introduction of particles into the material.

This is the case, for example, with the technology called SIMOX forproducing silicon-on-insulator substrates where the introduction ofoxygen atoms into a silicon material makes it possible, by the oxygenand silicon combining, to produce a buried SiO₂ layer. This process isdescribed in the following reference: “Silicon-on-Insulator Technology”,MRS Bulletin, December 1998, Volume 23, No. 12 (a publication of theMaterials Research Society).

In this reference, there is also a description of the process called“SMART-CUT” that uses particles to weaken the material because of thedefects created by the penetration of these particles into the materialand/or-because of the interaction of these defects with the atomsarising from the implanted particles.

French patents FR-A-9111491, FR-A-9315563, FR-A-9600852 and FR-A-9606086disclose various processes that cause a material to be weakened in thedepth, making it possible to cut off thin films of said material. Theseprocesses use hydrogen or rare-gas ion implantation possibly combinedwith one or more subsequent heat treatments in order to weaken thematerial at a depth close to the depth of penetration of the ions.

In the above processes, it is attempted, during the ion implantationphase that requires a specified temperature range, to prevent thetemperature from rising above a value of around 400° C. so that theimplanted species do not escape from the material. In these processesthat allow layers with a thickness of around 1 to 2 microns to beproduced in the silicon, even if the amount of energy used is high(around 1500 to 2000 joules per square centimeter (J/cm²)), this energyis applied for long periods (measuring in minutes) so that the meanpower is low enough for there to be no zone of high thermal energydensity and so that, by natural means of cooling or with conventionalcooling means on the implantation machines, the temperature of theimplanted material remains moderate.

Because of this very high amount of energy, the cost of the process ishigh. These techniques are in fact suitable for the production of thinfilms (up to about 2 microns) for very high value-added applications.However, they are not suitable for producing thicker films, since theamount of energy needed increases with the thicknesses and for example,reaches 10 000 to 20 000 J/cm² for a thickness of 10 microns, therebyvery considerably increasing the cost of the process.

There also exists in the prior art, processes in which materials areproduced that have, in the depth, a zone that is selectively absorbentrelative to the power flux used. For example, in the case of a laserbeam, a structure is produced that has, in the depth, a layer thatabsorbs at the wavelength of the laser, whereas the upper part issubstantially transparent or weakly absorbent at this wavelength.

More particularly, European patent EP-A-0 924 769 discloses a process inwhich structures are fabricated by the successive stacking of severallayers, one of which is capable of allowing separation from the materialat this layer. One particular example is indicated in which a layer richin hydrogen also has the property of being selectively absorbentrelative to the rest of the material in such a way that a laser beam candeposit its energy in this layer without significantly depositing energyin the other layers.

This manner of operating has the drawback and the limitation ofrequiring the fabrication of structured materials by the stacking oflayers with, located at the required depth, a layer that is selectivelyabsorbent relative to the power flux.

SUMMARY OF THE INVENTION

The present invention relates to a process for the treatment of acomponent with a view to modifying at least one of its properties, thisprocess being such that the invention is completely different from theprior art described above, both as regards the technical problems thatit poses and as regards the means that it employs and the results thatit allows to be obtained.

One objective of the present invention is to provide a treatment processfor modifying at least one property of the component in at least onezone to be treated located in the depth, that is to say at a distancefrom a surface of this component, without impairing or affecting theproperties of the component in the space separating this surface fromthe zone to be treated and further in the depth, beyond this zone to betreated.

Another objective of the present invention is to provide a treatmentprocess that in particular imposes no constraints either on the natureor on the structure of the constituent material or materials of thecomponent to be treated.

Another objective of the present invention is to provide a treatmentprocess whose operating cost is in particular relatively low.

Another objective of the present invention is to provide a treatmentprocess allowing, in particular, savings to be made as regards to theconstituent material or materials of the component to be treated.

Another objective of the present invention is to provide a treatmentprocess that can be applied especially in the field of membranes andthin films, especially semiconductor thin films, in the field of theproduction of wafers or plates of material, in the field of theproduction of semiconductor wafers or slices, especially those made ofsilicon, of semiconductors of the IV type, IV-IV type, III-V type andII-VI type, in order to obtain electronic or optoelectronic components,such as photovoltaic cells or elements, and in the field of the weldingor brazing of parts of a workpiece.

The subject of the present invention is a process for the treatment of acomponent, at least one zone to be treated of which located in the depthof this component at a certain distance from the surface thereof, has atleast one property that can be modified when this zone is subjected to athermal energy density above a specified treatment level.

According to the invention, this process consists in placing thecomponent to be treated at a thermal energy level below said specifiedlevel; and

in subjecting, through its aforementioned surface, for a specified timeand in the form of at least one pulse, said component to a power fluxgenerated by a particle emission means, this emission means beingregulated so as to produce a thermal energy density that is concentratedon or has a localized maximum in said zone to be treated and reaching,in at least part of this zone, a level above said specified treatmentlevel.

The process according to the invention preferably consists in choosing apower flux exclusively adapted for producing said thermal energydensity.

According to the invention, said specified thermal energy level mayadvantageously correspond to a specified temperature.

According to the invention, said component may advantageously be made ofa single material or of several parts of different materials.

According to the invention, said component may advantageously have asurface structure and/or a volume structure.

According to the invention, said power flux preferably consists of aflux of particles such as electrons and/or protons and/or ions and/oratoms and/or molecules.

According to the invention, said power flux may advantageously be formedby a flux of particles consisting or composed of elements of atomicnumber Z less than or equal to six, which are not dopants for theconstituent material or materials of said component, in any one of theirisotopic species, in any one of their molecular forms and in anyionization state, including the neutral state.

According to the invention, said particles may advantageously beessentially monokinetic.

According to the invention, the process may advantageously consist inchoosing a component whose zone to be treated includes impurities.

According to the invention, said impurities preferably have asegregation coefficient, relative to the constituent material of atleast said part to be treated, of less-than one.

According to the invention, the process may advantageously include aprior step of introducing said impurities into the material.

According to the invention, said step of introducing said impuritiespreferably includes at least one epitaxial growth.

According to the invention, said impurities may advantageously beintroduced at least partly during application of said power flux.

According to the invention, the constituent material of at least saidzone to be treated may advantageously comprise silicon and at least-saidzone to be treated contains impurities chosen from aluminium and/orbismuth and/or gallium and/or indium and/or antimony and/or tin.

According to the invention, the constituent material of at least saidzone to be treated may advantageously comprise silicon-germanium.

According to the invention, the process may advantageously consist insubjecting said component to a flux whose power is constant over time.

According to the invention, the process may advantageously consist invarying the intensity of the power flux.

According to the invention, the process may advantageously consist invarying the position of the concentrated part of said power fluxrelative to said zone to be treated.

According to a variant of the invention, said power flux is preferablychosen so as to liquefy the constituent material of said zone to betreated.

According to another variant of the invention, said power flux ispreferably chosen so as to produce inclusions in the constituentmaterial of said zone to be treated.

According to the invention, said inclusions may advantageously beprecipitates and/or bubbles and/or microbubbles and/or defects and/orchanges of phase and/or of chemical composition and/or fractures and/orcavities.

According to another variant of the invention, said power flux ispreferably chosen so as to weaken said zone to be treated.

According to another variant of the invention, said power flux ispreferably chosen so as to weld or braze together two parts of saidcomponent that are in contact in said zone to be treated.

The present invention will be better understood thanks to the followingnon-limiting explanations as regards the component to be treated.

The component to be treated may be of a bulk form or be in the form ofone or more thin layers, and be either homogeneous or heterogeneous inform and/or have a surface structure and/or a volume structure. Oneparticular example is a block of single-crystal silicon cutlongitudinally from a cylindrical ingot. Another example is a siliconwafer on which a silicon-germanium or silicon-germanium-carbon layer 500angstroms in thickness is grown, on which a five micron silicon layer isgrown.

The component may consist of at least two parts, made of one material orof different materials, in simple contact at a common surface thatconsequently constitutes an interface within this material. The powerflux used in the invention may be applied through one of the surfaces ofthe material-so as to create a zone of high thermal energy at thisinterface, for example to produce welding or brazing.

The material may also include impurities, defined as atoms or moleculesor particles, that are in a stable or metastable state, i.e. unable tochange discernibly, under, standard temperature conditions. In oneparticular, method implementation, the purpose of the treatment of thematerial having these impurities is to generate inclusions. Theinclusions may be particle agglomerates, bubbles, both of substantiallyspherical shape and of flattened shape, resulting for example from thevaporization of the material or from the impurities passing into a gasphase, precipitates of atoms or molecules, precipitates of defects,cavities structural defects, fractures, new chemical compounds, newphases, or any combination of these elements. The impurities may beeverywhere in the material, but must be at least partly in or near thetreatment zone.

One step of introducing said impurities into the material may beprovided prior to and/or during the treatment. For example, if thedesired impurity contains hydrogen, it may possibly be partly introducedduring application of the power flux if the latter consists of a flux ofhydrogen based particles. This introduction step may be carried outduring fabrication of the material or subsequently. In particular, insitu doping, diffusion, ion implantation, film deposition and epitaxialgrowth techniques may be used.

The present invention will also be better understood thanks to thefollowing non-limiting explanations as regards the power flux employed.

When a flux of power P is directed for a time Δt onto a material capableof absorbing this power, the material absorbs an amount of energy E_(a)equal to PΔt. If the intensity of the power flux is not constant overthe time Δt, the energy E_(a) absorbed may be calculated by dividing thetime Δt into time intervals δt in which the power flux may be consideredas being constant and adding the contributions corresponding to eachtime interval δt. The absorbed energy E_(a) density profile, i.e. thecurve representing the amount of energy absorbed per unit volume as afunction of the depth d, depends on the power flux parameters, i.e. theexperimental conditions and, in particular, the nature of the power fluxand of its characteristics, and also of the material itself.

If the power flux parameters vary over the course of time, the shape ofthe absorbed energy density profile varies over time. At a giveninstant, the absorbed energy density profile is obtained by taking intoaccount the contributions relating to each of the intervals δt.

In the case of a flux of particles, the kinetic energy of each particleor particle energy e is determined by its mass and its velocity, andthis kinetic energy e is generally measured in electron volts or amultiple of this unit. In the case of monokinetic particles that arecompletely absorbed in the material, the energy E_(a) is equal to Ne andthe power P is equal to Ne/Δt=E_(a)/Δt, where N is the number ofparticles that have been directed into the material during the timeinterval Δt. It is therefore obvious that the power is very stronglydependent on the time Δt, for the same value of absorbed energy E_(a)

During penetration of the particles into the material, the kineticenergy of these particles is extremely rapidly transformed in thematerial, through various physical mechanisms, such as electronexcitation (transfer of energy to electrons), phonon creation, orionization or displacement of atoms, or the breaking of chemical bonds,into essentially thermal energy, i.e. into heat. The increase in thethermal energy density is generally manifested by an increase in thetemperature and/or a supply of energy for activating physical and/orchemical reactions such as, for example, phase changes orchemical-reactions.

The effect of the power flux is therefore to create one or more thermalenergy sources. The heat or thermal energy in a material changesaccording to the known laws in physics, called the heat equations, thattake into account the thermal parameters of the material, the thermalconditions at the interfaces and at then surfaces, the initialconditions and the thermal energy sources that represent, at each pointin the material, the amplitude of the thermal energy density supplied tothe material as a function of time.

For example, the basic equations governing the physics of heat in solidswill be found in the reference document “Conduction Of Heat In Solids”,second edition, by H. S. Carslaw and J. C. Jaeger, Oxford UniversityPress, Walton Street, Oxford OX2 6DP. By solving these equations, it ispossible to determine the thermal energy density profile in the materialas a function of time, that is to say the temperature and the state ofthe various phases. To solve these equations in the general case must becarried out on a computer using numerical methods known per se, forexample using the finite-difference methods or the finite-elementmethod.

Generally speaking, the thermal energy density profile resulting from apulsed power flux directed onto the material is not in the steady state,i.e. it changes with time, during and after the time Δt, and its naturaltendency is to broaden.

For a given amount of thermal energy, the broadening that takes place isto the detriment of the thermal energy density level. Now, to treat amaterial in a specified zone it is necessary for the thermal energy inthe treatment zone to reach a sufficient level capable of activating thedesired process. It is therefore absolutely essential for the thermalenergy resulting from the power flux to be concentrated in the treatmentzone.

To achieve this, the solutions is, on the one hand, for the energy to beabsorbed in a depthwise concentrated manner in and/or near the treatmentzone and, on the other hand, for the duration of the power flux to besufficiently short and the intensity of the power flux to be high enoughfor the thermal energy profile to remain sufficiently concentrated andfor its level to be sufficient for the treatment of the material inquestion.

More precisely, according to the invention, it is preferred to use aflux of light particles chosen, possibly in combination, from electronsor ions or atoms or molecules consisting or composed of elements of lowatomic number Z, in any one of their isotopic species, in any one oftheir molecular forms and in any ionization state, including the neutralstate. The expression “elements of low atomic number Z” is understood tomean those in which Z, i.e. the number of protons in the nucleus, isless than or equal to 6. In particular, Z will be chosen to be less than3 and preferably equal to 1, corresponding to hydrogen. This is because,for said light particles, it is possible to find conditions such that,during their penetration into a material, these particles transferenergy to the material in the form of a profile concentrated at acertain depth. These conditions correspond to particles with a particleenergy that is higher the higher their Z. For example, it is possible toobtain a deposited energy profile having a peak at a depth ofapproximately 20 microns with 1.2 MeV protons or 5 MeV helium ions or 10MeV lithium ions or 25 MeV carbon ions. For a given maximum depth, theseprofiles are generally narrower the lower the atomic number Z of theparticle.

To avoid any problem of undesirable doping when the material is asemiconductor, these particles are chosen from those that are notdopants for said material. For example, in the case in which thematerial is silicon, if it is desired not to create p-doping, then boronis excluded.

In the case of electrons, it is possible to calculate, using suitablesoftware, the distribution of the energy density as a function of thedepth in a material subjected to a flux of monoenergetic electrons. Thisdistribution may also be found directly in databases such as EMID(Electron Material Interaction Database) published by IDEA (Institutefor Data Evaluation) and the Radiation Dynamics Group (RDG) of KharkovNational University of Ukraine. A profile having a bell-shaped curve isobtained, having a maximum at a depth that depends on the energy of theelectrons. FIG. 2 a gives the energy deposition profile for 40 keVelectrons in silicon. This calculation is carried out under theassumption that the dimensions of the electron flux over the surface aresubstantially larger than the lateral dispersion of the electron path inthe material. In the above example, this assumption is justifiedwhenever the dimensions of the electron flux over the surface of thematerial are appreciably greater than 10 microns. Otherwise, the shapeof the curve depends on the dimensions of the flux; however, the sametype of calculation may be carried out and does give a curve of similarshape.

The table below gives the calculated approximate values of the depth ofthe maximum in the energy deposition profile in the case of silicon.Energy (in keV) 5 10 20 40 60 100 Depth (in microns) 0.11 0.33 1.2 4 820

The process may be carried out using protons, that is to say hydrogenions. Other types of light particles may be used, althoughimplementation of the method is more favorable when a narrow energydeposition profile with particles of the lowest possible Z is desired.

The penetration of ions into a material is accompanied essentially bytwo braking mechanisms, namely “electronic braking” and “nuclearbraking”. To simplify matters, nuclear braking contributes essentiallyto transferring energy to the atoms of the material and electron brakingcontributes essentially to transferring energy to the electrons of thematerial. Using simulation software, such as TRIM or SRIM, it ispossible to calculate the distribution of the absorbed energy density asa function of the depth in a material subjected to a flux ofmonoenergetic particles. A bell-shape profile having a maximum of adepth that depends on the energy of the particles is obtained. It isimportant to note that this absorbed energy deposition profile is ingeneral different from that of the concentration profile of the species,which represents the density of the implanted species as a function ofthe depth, and is also different from the density profile of the defectscreated.

It may be observed that the more monokinetic the particle flux, thenarrower the energy deposition peak and the more concentrated theenergy. If it is desired for the energy deposition to have a broaderpeak, or even several peaks, it is possible to use particles ofdifferent energies, or even different particles.

To obtain a zone of high thermal energy density in the treatment zone,it is therefore necessary:

-   -   to choose particle flux parameters such that most of this power        is deposited in/or near the treatment zone;    -   to choose a time Δt, during which the power flux is directed        onto the material, that is short enough for the thermal energy        resulting from the primary energy to be able to build up in and        near the treatment zone before it diffuses away from this zone;        and    -   to choose the intensity of the particle flux so that, during the        time Δt, the energy supplied by the particles is sufficient for        said thermal energy density level to be reached in the treatment        zone.

The time Δt may be calculated by simulation using known suitablesoftware, generally using finite-difference methods or finite-elementmethods.

Another way of determining this time is a method that is simpler toimplement. It consists firstly in roughly determining the value of themaximum time and then in adjusting it by means of several experiments.For a rough determination, we consider the root mean square deviationσ_(p) of the energy deposition profile resulting from the interaction ofthe particle flux with the material and the root mean square deviationσ_(t) of the desired thermal energy profile (σ_(t) is necessarily atleast equal to σ_(p)).

Next, the time Δt is estimated from the following inequality:2L _(t) ²=2DΔt<σ _(t) ²−σ_(p) ²in which L_(t) is the thermal diffusion length and D is the thermaldiffusivity at the temperature in question. This calculation gives abetter approximation the more σ_(t) exceeds σ_(p).

For example, in silicon in which the thermal diffusivity at hightemperature is of the order of 0.1 cm²/s for a desired thermal energyprofile with a root square deviation σ_(t) of 3 microns and an absorbedenergy profile with a root square deviation σ_(p) of the order of 1micron, this corresponds to a maximum time Δt of around 0.4microseconds.

When Δt is known, it is then possible for the shape of the thermalenergy density profile in the material to be determined precisely and,since the level to be reached in the treatment zone is known, it ispossible by numerical integration to deduce therefrom the total amountof thermal energy and therefore to determine the necessary powerintensity level over the time Δt.

The flux must therefore be in the form of a pulse of a high power andshort duration so that the required thermal energy level is reached inthe layer to be treated. If the treatment of the material requires alonger time than that permitted by a single pulse, it is possible toapply several pulses so that the cumulative time is suited to thetreatment.

Additionally, but not necessarily, it may be advantageous for certaintypes of process not only to control the duration of the high thermalenergy level but also to control the rise and/or fall of the thermalenergy level. To do this, it is possible to modulate the amplitude ofthe pulse as a function of time.

To produce a power flux in the form of a pulse, several methods ofimplementation are possible:

-   -   use of a power flux that is spatially constant with respect to        the material to be treated, the intensity of which as a function        of time is in the form of one or more pulses;    -   use of a power flux whose intensity as a function of time is        constant, but the position of which varies with respect to the        material so that a given region of the material sees the flux        only for one or more time intervals corresponding to the        duration of the desired pulse (or of the desired pulses); and    -   a combination of the two above methods of implementation.

To produce a power flux whose position varies with respect to thematerial, that is to say with respect to the treatment zone andapproximately perpendicular to the latter, it is possible, for example,to produce the particle flux in the form of concentrated beams (using,for example, a quadrople lens focussing system) and by means of a systemusing time-dependent electromagnetic forces (for example by means ofcoils) and to move the beam relative to the material (scanning), i.e.relative to the treatment zone and perpendicular to the latter. In thereference article “Focused MeV Ion Beams for Materials Analysis andMicrofabrication”, MRS BULLETIN, February 2000, Volume 25, No. 2 (apublication of the Materials Research Society), page 33 to 37, anexample of equipment for producing focused scanned proton beams is givenon page 34 in figure 2. Although the application described in thatexample does not relate to the present invention, the principles used togenerate the proton beam and to move it relative to the material may beused for our invention.

However, it should be noted that, that to produce beams for obtainingthe desired current density, it is necessary for the energy of theprotons to exhibit little dispersion. Otherwise, chromatic aberrations(owing to the dispersions in the energy of the protons and thereforedispersion in their velocity) would broaden the focal spot. It istherefore recommended to make use of an ion accelerator capable of lowenergy dispersion. Conventional electrostatic accelerators of the Van DeGraaff type, with electrical charge transport by belts or chains, arevery limited in this field. An electrostatic accelerator of thesingletron type sold by HVEE (High Voltage Engineering Europa BV) bettermeets the requirements as it allows energy dispersions within the 10⁻5range. Further details will be found in the following reference article:“The novel ultrastable HVEE 3.5 MeV singletron accelerator for nanoprobeapplications”, D. J. W. Mous, R. G. Haitsma, T. Butz, R.-H. Flagmeyer,D. Lehmann and J. Vogt in Nuclear Instruments and Methods in PhysicsResearch B 130, 31-36, (1997).

It is also possible to leave the beam fixed in space and to move thecomponent relative to the beam, for example by fastening-this componentto a wheel that rotates at high speed. In one non-limiting embodiment, a1 MeV proton beam is formed with a diameter of about 100 microns and acurrent of about 2.6 mA. This beam is directed onto silicon wafersfastened to the peripheral part of the surface of a disk about 2 m indiameter rotating at a speed of about 3 200 rpm (FIG. 4). Under theseconditions, upon passing beneath the beam any point on the waferreceives a power flux pulse of about 0.3 microseconds duration. Thispulse is suitable for the thermal energy density reached between a depthof 12 microns and a depth of 17 microns to be around 7000 J/cm³. Therotation movement of the disk may be combined with a displacementmovement of the spindle of the disk parallel to itself so that thetreatment with the proton flux can be applied, for example, at eachpoint on the wafers.

To produce a power flux whose intensity as a function of time is in theform of one or more pulses, it is possible to use, for example in thecase of protons, a machine operating according to the principles ofcertain machines used for heating plasmas by the injection of an intensepulsed beam of particles. In general, these machines comprise means forproducing a very dense plasma, means for extracting and accelerating theions in a very high electric field and, optionally, means for preventingany breakdown (arc formation) in the extracting and accelerating gaps,for example by the use of judicially positioned magnetic fields(magnetic isolation of the accelerating gaps). An example of suchequipment is described in the John B. Greenly patent US-RE-37,100. Inthe case of electrons, it is possible to use a machine of the typedescribed in the reference article “Principles of high current electronbeam acceleration”, Stanley Humphries Jr., Nuclear Instruments andMethods in Physics Research A258(1987) 548-565.

Alternatively, the electron beam may be generated by means of anelectron gun having a cold emission cathode of the microtip type withthe associated electrode or electrodes, similar to those used in flatscreens (field emission displays) based on microtips.

The following non-limiting example shows how to realize the principlesof the invention. The material is a single-crystal silicon wafer 200 mmin diameter and about 750 microns in thickness. The surface may or maynot be covered with thin films. This material contains antimony atomswith a concentration, for example, of around 10¹⁶ cm⁻³ to 2×10¹⁹ cm⁻³.With a power flux transported by a 1 MeV proton beam, the surface isirradiated with a current density of 50 A.cm⁻² for a time of 0.2microseconds.

An energy of around 10 J.cm⁻² is thus deposited. A zone between a depthof about 12 microns and a depth of about 17 microns is thus created inwhich the thermal energy density level reached is greater than or equalto about 7000 J.cm⁻³ . These values are given as a starting point. Afine adjustment may be made in order to take into account the changewith time of the power flux pulse and the thermal conditions of thematerial, in particular at its surface.

This thermal energy density level is sufficient to activate the desiredmaterial treatment described below.

The thermal energy density level reached makes it possible to liquefythe material in a treatment zone lying between a depth of about 12microns and a depth of about 17 microns, the extension of which-zone, ina plane parallel to the surface through which the power flux isintroduced, is defined by the lateral dimensions of this flux, thusdefining a liquid zone bounded by a solid/liquid interface above theapproximately 12 micron depth and a solid/liquid interface below the 17micron depth.

Most of the antimony atoms pre-existing in the solid phase in this zone,or near it, are in the liquid phase. Upon resolidification that occursduring cooling, the two solid/liquid interfaces each advance at theirown rate toward each other (FIG. 6), thus reducing the width of theliquid zone.

Because of the low value of the segregation coefficient (sometimescalled the distribution coefficient) of antimony in silicon, that is tosay because of the tendency of antimony atoms to remain in the liquidphase rather than passing into the solid phase, the advance of the twosolid/liquid interfaces has the effect of pushing the antimony atoms infront of them into the liquid phase, thus resulting in an ever greaterconcentration of antimony atoms in the liquid phase.

When the liquid phase has disappeared, all the antimony atoms arenecessarily in the material in the solid state. This results locally ina very high concentration of impurities in a narrow zone near the depthreferred to as the meeting depth, at which the two solid/liquidinterfaces meet and therefore at which the liquid phase completelydisappears.

Under judicially chosen experimental conditions, it is possible then tobe in a situation in which the antimony atoms are at a concentrationsuch that these atoms can no longer be normally incorporated into thesolid phase, thus giving rise to precipitates., structural defects,formation of heterogeneous mixtures, etc. It is thus possible to weakenthe material through this mechanism and achieve a separation betweenthat part of the material lying between the surface and the weakenedzone and the rest of the material.

It should be noted that, after the treatment, the sub-surface part ofthe material, lying between the surface and the high thermal energyzone, remains in the solid and crystalline state in accordance with thebasic principles of the invention and that the part of the materiallying between the subsurface zone and the vicinity of the meeting frontmay retain its crystalline properties, since the material may undergoepitaxial regrowth during the resolidification phase from the solidcrystalline material of the subsurface zone.

The resolidification phenomenon may be more complex than that describedabove since the advance of the two —upper and lower —interfaces may becombined with an advance of the lateral interfaces, and even with theformation of discontinuous liquid zones separated by resolidified zones.However, whatever the complexity of the mechanisms involved, this alwaysresults in the impurities being concentrated in a very small volume ofmaterial.

In this example, the antimony atoms may have been introduced duringgrowth of the ingot from which the wafer was obtained, giving anapproximately homogeneous concentration throughout the volume. Theantimony atoms may, in another method of implementation, be, forexample, in a subsurface layer some 20 microns in thickness. In thelatter case, this high antimony concentration may be obtained: bygrowing an antimony-doped layer 20 microns in thickness by epitaxy on ascarcely doped or undoped silicon substrate.

It is also possible in a different manner to use a highly antimony-dopedsilicon wafer on which a single-crystal layer of scarcely or lightlydoped silicon is grown by epitaxy, if it is desired to preserve alightly doped layer on the surface in order to fabricate devices. Thethickness of this scarcely doped layer in the particular case indicatedabove (1 MeV protons) may have a thickness of up to around twelvemicrons.

While keeping a lightly doped surface layer, it is also possible to havelocalized antimony doping within a deep layer. This is obtained forexample by producing, on the surface of a wafer, an antimony-doped layer(for example, by 10¹⁵ cm⁻² ion implantation at 150 keV followed by adiffusion heat treatment of 6 hours at 1150° C.), followed by epitaxialgrowth of scarcely doped or undoped silicon with a thickness of aroundtwelve microns.

In the above example, antimony atoms were used. The principle alsooperates with other atoms having a low segregation coefficient relativeto silicon, such as for example, but implying no limitation, aluminum,bismuth, gallium, indium and tin.

The choice of other impurities or atoms is possible. This choice dependson the constraints of the intended application. For example, an atomsuch as antimony will be chosen if it is desired for the residual dopingof the treated zone to be of the n type, while an atom such as aluminumwill be chosen if it is desired for the residual doping of the treatedzone to be of the p type.

In all these examples, in which epitaxial growth is used, the epitaxialprocess may either be a process of the CVD type or a process of theliquid phase epitaxy type; in particular, a liquid phase epitaxy ofsilicon from a bath of molten tin or aluminum or indium in which siliconhas been dissolved, may be one of the preferred ways of producingphotovoltaic cells.

To illustrate, generally and schematically, the present invention and inparticular the above examples and explanations, reference may be made tothe appended FIG. 1 which shows, in cross section, a component 1 ofparallelepipedal shape, that has a front flat surface 2 at a certaindistance away from which an apparatus 3 for emitting a particle flux 4is installed.

This power flux 4 is introduced into the component 1 perpendicular toits surface 2 and produces, in the component 1, a thermal energy densitywhose profile or curve 5 at the end of the power flux pulse has beenshown. The profile 5 is, parallel to the surface 2, approximately in theform of a bell or a peak, and the maximum of this profile 5 lies in atreatment zone 6 localized in the depth at a certain distance from thesurface 2 of the component 1. Of course, the power flux 4 could beintroduced into the component 1 at another angle of incidence than thatcorresponding to normal incidence.

With a component 1 placed at a thermal energy level below the specifiedtreatment level 7, in particular at a temperature below a specifiedtreatment value, the thermal energy density 5 produced by the power flux4 exhibits a peak 5 a that reaches the specified treatment level 7 andexceeds-this level over a thickness d such that at least one property ofthe constituent material of the zone 6 to be treated is modified in thisthickness d and over the surface corresponding approximately to thecross section of the power flux 4. It follows that the properties of therest of the component 1, and in particular its part 8 lying between thesurface 2 and the zone 6 and its part 9 lying beyond this zone 6 are notimpaired or modified.

FIG. 2 a shows a curve 10 that represents the approximately bell-shapedprofile of the energy density deposited as a function of the depth,produced in a silicon wafer by an electron flux and FIG. 2 b shows acurve 11 that represents approximately the depth of the maximum energydensity deposited by an electron flux or electron beam in a siliconwafer.

FIG. 3 shows a curve 12 that represents the profile, with a pronouncedpeak, of the deposited energy density as a function of the depth,produced in a silicon wafer by a proton flux.

FIG. 4 shows, in side view and from above, a treatment apparatus 13 thatcomprises a rotating plate 14 on which a component 1 to be treated isplaced between its center and its edge. The component 1 passes in frontof a power flux 4 in such a way that this component 1 is subjected, ateach revolution of the plate 14, to a pulse of the power flux 4. Thenumber of revolutions that the plate 14 must perform depends on thetreatments to be obtained that were described above.

FIG. 5 shows, in cross section, a component 1 to be treated, formed by awafer from which it is desired to extract slices 15.

To do this, a particle flux 4 is applied that weakens the material in azone 6 to be treated at a depth away-<from its surface 2, correspondingto the thickness of the desired slice, in such a way that this slice 15is thus separable.

In an example, this arrangement is particularly advantageous from atechnical standpoint and from a cost standpoint for producing thinsilicon photovoltaic cells, in particular with a thickness of the orderof 10 to 100 microns.

FIG. 6 shows the component 1 to be treated, formed by two parts-16 and17 that are in contact via an interface 18 and that it is desired toweld or braze.

To do this, a particle flux 4 is applied that causes a temperature riseand/or melting in a zone 6 to be treated that includes the interface 18,suitable for welding or brazing the two parts 16 and 17 to each other.

FIG. 7 shows, in cross section, a component 19, for example made ofsilicon containing impurities having a segregation coefficient of lessthan 1 relative to silicon, such as antimony, aluminum, bismuth,gallium, indium or tin.

As described with reference to FIG. 1, a pulsed proton flux 4 isapplied, the flux being introduced into the component 19 through itssurface 20, the deposited energy density-having a profile correspondingto that shown in FIG. 3.

By tailoring the conditions of application of the proton flux 4 for thispurpose, liquefaction of the silicon occurs in a zone 21 to be treatedlying in the depth and located within the region of the peak of thedeposited energy profile.

The liquid silicon phase 21 a contained approximately between twosolid/liquid interfaces 22 and 23 approximately parallel to the surface20 progressively increases in thickness during the application of theproton flux 4, as shown by the arrows 24 and 25 attached to theinterfaces, before reaching the maximum.

Because of the thermal diffusion in the rest of the component 19, theliquefaction phase is followed by a silicon resolidification phase thatresults in a progressive reduction in the distance between theinterfaces 22 and 23, as shown by the arrows 26 and 27 attached to theseinterfaces. This resolidification phase generally, and essentially,occurs after the pulse of the proton flux 4 has been applied.

During the aforementioned silicon liquefaction phase, the impuritiespass into solution in the liquid phase 21 a.

During the aforementioned silicon resolidification phase, the impuritieshave a tendency to remain in the liquid phase 21 a in such a way that,at the end of the silicon resolidification phase, these impurities areconcentrated in the part 21 b of the zone 21 to be treated thatresolidifies last, i.e. in a silicon volume whose thickness is much lessthan the afore-mentioned maximum thickness of the liquid phase 21 a.

These impurities may therefore be in the part 21 b with concentrationlevels much higher than that of the solubility limit in the solid phase,thus forming precipitates and/or crystal defects that weaken the siliconin the concentration zone. The weakened part 21 b may then constitute azone for separating or breaking the component 19 into two parts.

The present invention is not limited to the examples described aboveMany alternative versions are possible without departing from the scopeof the appended claims.

1. A process for the treatment of a component, at least one zone to betreated of which, located in the depth of this component at a certaindistance from the surface thereof, has at least one property that can bemodified when this zone is subjected to a thermal energy density above aspecified treatment level, characterized in that it consists: in placingthe component (1) to be treated at a thermal energy level below saidspecified level (7); and in subjecting, through its aforementionedsurface, for a specified time and in the form of at least one pulse,said component to a power flux (4) generated by a particle emissionmeans (3), this emission means being regulated so as to produce athermal energy density (5) that is concentrated on or has a localizedmaximum in said zone to be treated and reaching, in at least part ofthis zone, a level above said specified treatment level.
 2. The processof claim 1, and choosing a power flux exclusively adapted for producingsaid thermal energy density.
 3. The process of claim 1, in which saidspecified thermal energy level corresponds to a specified temperature.4. The process of claim 1, in which said component is made of a singlematerial or of several parts of different materials.
 5. The process ofclaim 1, in which said component has a surface structure and/or a volumestructure.
 6. The process of claim 1, in which said power flux consistsof a flux of particles such as electrons and/or protons and/or ionsand/or atoms and/or molecules.
 7. The process of claim 1, in which saidpower flux is formed by a flux of particles consisting or composed ofelements of atomic number Z less than or equal to six, which are notdopants for the constituent material or materials of said component, inany one of their isotopic species, in any one of their molecular formsand in any ionization state, including the neutral state.
 8. The processof claim 1, in which said particles are essentially monokinetic.
 9. Theprocess claim 1, and choosing a component whose zone to be treatedincludes impurities.
 10. The process of claim 9, of which saidimpurities have a segregation coefficient, relative to the constituentmaterial of at least said part to be treated, of less than one.
 11. Theprocess of claim 9, and performing a prior step of introducing saidimpurities into the material.
 12. The process of claim 9, in which saidstep of introducing said impurities includes at least one epitaxialgrowth.
 13. The process of claim 9, in which said impurities areintroduced at least partly during application of said power flux. 14.The process of claim 1, in which the constituent material of at leastsaid zone to be treated comprises silicon and in that at least said zoneto be treated contains impurities chosen from aluminium and/or bismuthand/or gallium and/or indium and/or antimony and/or tin.
 15. The processof claim 1, in which the constituent material of at least said zone tobe treated comprises silicon-germanium.
 16. The process of claim 1, andsubjecting said component to a flux whose power is constant over timeand the position of which varies with respect to the material so that agiven region of the material sees the flux only for one or more timeintervals corresponding to the duration of the desired pulses.
 17. Theprocess of claim 1, and in which the power flux is spatially constantwith respect to the material to be treated and the intensity thereof isin the form of one or more pulses so as to vary the as a function oftime.
 18. The process of claim 1, and varying the position of theconcentrated part of said power flux relative to said zone to betreated.
 19. The process of claim 1, in which said power flux is chosenso as to produce a thermal energy density above the said specifiedthermal energy level corresponding to the liquefaction of theconstituent material of said zone to be treated.
 20. The process ofclaim 1, in which said power flux is chosen so as to produce a thermalenergy density above the said specified thermal energy level having theeffect of generating inclusions in the constituent material of said zoneto be treated.
 21. The process of claim 20, in which said inclusions areprecipitates and/or bubbles and/or microbubbles and/or defects and/orchanges of phase and/or of chemical composition and/or fractures and/orcavities.
 22. The process of claim 1, in which said power flux is chosenso as to product a thermal energy density above the said specifiedthermal level having the effect of weakening said zone to be treated.23. The process of claim 1, in which said power flux is chosen so as toproduce a thermal energy density above the said specified thermal levelhaving the effect of welding or brazing together two parts of saidcomponent that are in contact in said zone to be treated.
 24. A processfor the treatment of a component, at least one zone to be treated ofwhich, located in the depth of this component at a certain distance fromthe surface thereof, has at least one property that can be modified whenthis zone is subjected to a thermal energy density above a specifiedtreatment level corresponding to a specified temperature level,consisting of: placing the component (1) to be treated at a temperaturelevel below said specified temperature level (7); and subjecting,through its aforementioned surface, for a specified time and in the formof at least one pulse, said component to a power flux (4) generated by aparticle emission means (3), and in which said emission means areregulated so as to produce a thermal energy density (5) that isconcentrated on or has a localized maximum in said zone to be treatedand reaching, in at least part of this zone, a level above saidspecified temperature level.
 25. The process of claim 24, in which saidpower flux consists of a flux of particles such as electrons and/orprotons and/or ions and/or atoms and/or molecules.
 26. The process ofclaim 24, in which said power flux is formed by a flux of particlesconsisting or composed of elements of atomic number Z less than or equalto six, which are not dopants for the constituent material or materialsof said component, in any one of their isotopic species, in any one oftheir molecular forms and in any ionization state, including the neutralstate.
 27. A process for the treatment of a component, at least one zoneto be treated of which, located in the depth of this component at acertain distance from the surface thereof, has at least one propertythat can be modified when this zone is subjected to a thermal energydensity above a specified treatment level, consisting of: placing thecomponent (1) to be treated at a thermal energy level below saidspecified level (7); and subjecting, through its aforementioned surface,for a specified time and in the form of at least one pulse, saidcomponent to a power flux (4) chosen so as to produce a thermal energydensity above the said specified thermal energy level corresponding tothe liquefaction of the constituent material of said zone to be treatedand generated by a particle emission means (3) consisting of a flux ofparticles such as electrons and/or protons and/or ions and/or atomsand/or molecules, and in which said emission means are regulated so asto produce a thermal energy density (5) that is concentrated on or has alocalized maximum in said zone to be treated and reaching, in at leastpart of this zone, a level above said specified treatment levelcorresponding to the said liquefaction.
 28. The process of claim 27, inwhich said particles are essentially monokinetic.
 29. A process for thetreatment of a component, at least one zone to be treated of which,located in the depth of this component at a certain distance from thesurface thereof, has at least one property that can be modified whenthis zone is subjected to a thermal energy density above a specifiedtreatment level, consisting of placing the component (1) to be treatedat a thermal energy level below said specified level (7); andsubjecting, through its aforementioned surface, for a specified time andin the form of at least one pulse, said component to a power flux (4)chosen so as to produce a thermal energy density above the saidspecified thermal energy level corresponding to the liquefaction ofpermitting to liquefy the constituent material of said zone to betreated and generated by a particle emission means (3), this emissionmeans being regulated so as to produce a thermal energy density (5) thatis concentrated on or has a localized maximum in said zone to be treatedand reaching, in at least part of this zone, a level above saidspecified treatment level corresponding to the said liquefaction; and inwhich said power flux is formed by a flux of particles consisting orcomposed of elements of atomic number Z less than or equal to six, whichare not dopants for the constituent material or materials of saidcomponent, in any one of their isotopic species, in any one of theirmolecular forms and in any ionization state, including the neutralstate.
 30. The process of claim 29, in which said particles areessentially monokinetic.
 31. A process for the treatment of a component,at least one zone to be treated of which, located in the depth of thiscomponent at a certain distance from the surface thereof, has at leastone property that can be modified when this zone is subjected to athermal energy density above a specified treatment level, in which saidcomponent is chosen so as to includes at least in said zone impuritieshaving a segregation coefficient, relative to the constituent materialof at least said part to be treated, of less than one and consisting ofplacing the component (1) to be treated at a thermal energy level belowsaid specified level (7); and subjecting, through its aforementionedsurface, for a specified time and in the form of at least one pulse,said component to a power flux (4) chosen so as to produce a thermalenergy density above the said specified thermal energy levelcorresponding to the liquefaction of the constituent material of saidzone to be treated and generated by a particle emission means (3), thisemission means being regulated so as to produce a thermal energy density(5) that is concentrated on or has a localized maximum in said zone tobe treated and reaching, in at least part of this zone, a level abovesaid specified treatment level corresponding to the said liquefaction.32. The process of claim 31, in which the constituent material of atleast said zone to be treated comprises silicon and in that at leastsaid zone to be treated contains impurities chosen from aluminium and/orbismuth and/or gallium and/or indium and/or antimony and/or tin.
 33. Theprocess of claim 31, in which the constituent material of at least saidzone to be treated comprises silicon-germanium.
 34. A process for thetreatment of a component, at least one zone to be treated of which,located in the depth of this component at a certain distance from thesurface thereof, has at least one property that can be modified whenthis zone is subjected to a thermal energy density above a specifiedtreatment level, consisting of placing the component (1) to be treatedat a thermal energy level below said specified level (7); andsubjecting, through its aforementioned surface, for a specified time andin the form of at least one pulse, said component to a power flux (4))chosen so as to produce a thermal energy density above the saidspecified thermal energy level corresponding to the liquefaction of theconstituent material of said zone to be treated and generated by aparticle emission means (3), in which this emission means are regulatedso as to produce a thermal energy density (5) that is concentrated on orhas a localized maximum in said zone to be treated and reaching, in atleast part of this zone, a level above said specified treatment levelcorresponding to the said liquefaction; and in which the power flux isconstant over time and the position of which varies with respect to thematerial so that a given region of the material sees the flux only forone or more time intervals corresponding to the duration of the desiredpulses.
 35. The process of claim 34, in which said power flux consistsof a flux of particles such as electrons and/or protons and/or ionsand/or atoms and/or molecules.
 36. The process of claim 34, in whichsaid power flux is formed by a flux of particles consisting or composedof elements of atomic number Z less than or equal to six, which are notdopants for the constituent material or materials of said component, inany one of their isotopic species, in any one of their molecular formsand in any ionization state, including the neutral state.
 37. A processfor the treatment of a component, at least one zone to be treated ofwhich, located in the depth of this component at a certain distance fromthe surface thereof, has at least one property that can be modified whenthis zone is subjected to a thermal energy density above a specifiedtreatment level, consisting of: placing the component (1) to be treatedat a thermal energy level below said specified level (7); andsubjecting, through its aforementioned surface, for a specified time andin the form of at least one pulse, said component to a power flux (4))chosen so as to produce a thermal energy density above the saidspecified thermal energy level corresponding to the liquefaction of theconstituent material of said zone to be treated and generated by aparticle emission means (3), in which this emission means beingregulated so as to produce a thermal energy density (5) that isconcentrated on or has a localized maximum in said zone to be treatedand reaching, in at least part of this zone, a level above saidspecified treatment level corresponding to the said liquefaction; and inwhich the power flux is spatially constant with respect to the materialto be treated and the intensity thereof is in the form of one or morepulses so as to vary the as a function of time.
 38. The process of claim37, in which said power flux consists of a flux of particles such aselectrons and/or protons and/or ions and/or atoms and/or molecules. 39.The process of claim 37, in which said power flux is formed by a flux ofparticles consisting or composed of elements of atomic number Z lessthan or equal to six, which are not dopants for the constituent materialor materials of said component, in any one of their isotopic species, inany one of their molecular forms and in any ionization state, includingthe neutral state.
 40. A process for the treatment of a component, atleast one zone to be treated of which, located in the depth of thiscomponent at a certain distance from the surface thereof, has at leastone property that can be modified when this zone is subjected to athermal energy density above a specified treatment level, consisting of:placing the component (1) to be treated at a thermal energy level belowsaid specified level (7); and subjecting, through its aforementionedsurface, for a specified time and in the form of at least one pulse,said component to a power flux (4) chosen so as to produce a thermalenergy density above the said specified thermal energy level having theeffect of generating inclusions in the constituent material of said zoneto be treated and generated by a particle emission means (3), in whichthis emission means are regulated so as to produce a thermal energydensity (5) that is concentrated on or has a localized maximum in saidzone to be treated and reaching, in at least part of this zone, a levelabove said specified treatment level having the effect of generating thesaid inclusions.
 41. The process of claim 40, in which said specifiedthermal energy level corresponds to a specified temperature.
 42. Theprocess of claim 40, in which the constituent material of at least saidzone to be treated comprises silicon and in that at least said zone tobe treated contains impurities chosen from aluminium and/or bismuthand/or gallium and/or indium and/or antimony and/or tin.
 43. The processof claim 40, in which the constituent material of at least said zone tobe treated comprises silicon-germanium.
 44. A process for the treatmentof a component, at least one zone to be treated of which, located in thedepth of this component at a certain distance from the surface thereof,has at least one property that can be modified when this zone issubjected to a thermal energy density above a specified treatment level,consisting of: placing the component (1) to be treated at a thermalenergy level below said specified level (7); and subjecting, through itsaforementioned surface, for a specified time and in the form of at leastone pulse, said component to a power flux (4) chosen so as to produce athermal energy density to produce a thermal energy density above thesaid specified thermal level having the effect of weakening said zone tobe treated and generated by a particle emission means (3), and in whichsaid emission means are regulated so as to produce a thermal energydensity (5) that is concentrated on or has a localized maximum in saidzone to be treated and reaching, in at least part of this zone, a levelabove said specified treatment level having the effect of the saidweakening.
 45. The process of claim 44, in which said specified thermalenergy level corresponds to a specified temperature.
 46. The process ofclaim 44, in which the constituent material of at least said zone to betreated comprises silicon and in that at least said zone to be treatedcontains impurities chosen from aluminium and/or bismuth and/or galliumand/or indium and/or antimony and/or tin.
 47. The process of claim 44,in which the constituent material of at least said zone to be treatedcomprises silicon-germanium.